Sintering furnace for producing an HTSC strip

ABSTRACT

The invention relates to a method for producing a high temperature superconductor (HTSC) from a strip including an upper side precursor layer and which, for continuous sintering of the precursor layer within a furnace in the presence of a fed-in reaction gas, is drawn across a support. A furnace for performing the method is also described.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.12/031,939, filed on 15 Feb. 2008 now U.S. Pat. No. 7,964,533 andentitled “Method for Producing an HTSC Strip,” which claims priorityunder 35 U.S.C. §119 to Application No. DE 102007007567.9, filed on 15Feb. 2007 and entitled “Method for Producing an HTSC Strip.” Thedisclosures of each of the above applications are hereby incorporated byreference in their entireties.

FIELD OF THE INVENTION

The invention relates to a method for producing a high temperaturesuperconductor (HTSC) from a strip which has an upper side precursorlayer, wherein the strip is drawn across a support for continuoussintering of the strip within a furnace in the presence of a fed-inreaction gas.

BACKGROUND OF THE INVENTION

In a conventional process for preparing a multi-layer superconductorarticle, a reactor (e.g., a tube furnace) includes a housing having anupper wall with passages (e.g., slots or nozzles) that are in fluidcommunication with gas mixture sources (e.g., oxygen, water, and one ormore inert gases (e.g., nitrogen, argon, helium, krypton, xenon). Asubstrate, which is wound around reels, moves through reactor in apredetermined direction.

As a substrate enters the reactor, it passes through a various regionswithin the reactor, during which time the gas mixture is directeddownward, toward substrate. A film containing a precursor (e.g., asuperconductor precursor film containing barium fluoride and/oradditional materials, such as CuO and/or Y₂O₃) is present on the surfaceof substrate, moving through the regions of the reactor. The precursoris exposed to the gas mixture, reacting therewith. Spent reaction gas isdrawn-off by a pump that directs the spent gas through a through aporous material positioned adjacent the passages (the slots or nozzles)in the upper wall.

In the conventional system using the above process, fresh and usedreaction gases are mixed without control. This, in turn, leads toimpairment of quality of the HTSC layer and/or long retention times ofthe strip in the furnace. Thus, it would be desirable to develop an HTSCformation method that controlled to level of mixing between the freshand used reaction gases.

OBJECTS AND SUMMARY OF THE INVENTION

One object of the invention is to provide a method of forming astrip-shaped HTSC of constant high quality. Another object of theinvention is to provide a reactor/furnace for performing a method ofthis kind. The above and still further objects, features, and advantagesof the present invention will become apparent upon consideration of thefollowing descriptions and descriptive figures of specific embodimentsthereof, wherein like reference numerals in the various figures areutilized to designate like components. While these descriptions go intospecific details of the invention, it should be understood thatvariations may and do exist and would be apparent to those skilled inthe art based on the descriptions herein.

In accordance with the invention, a strip having a precursor layer isdrawn across a porous support through which fresh reaction gas iscontinuously fed. The continuous feeding forms a laminar flow of thefresh reaction gas above the porous support and along the sides of thestrip. A vortex zone forms above the strip in the flow shadow of thestrip. In the boundary region between the vortex zone and the regions oflaminar flow adjacent/lateral to the vortex zone, a continuous exchangeof gas takes place between the vortex zone and the laminar flow. As aresult, the vortex zone is always sufficiently enriched with freshreaction gas. In this manner, the vortices ensure good mixing of freshand used reaction gas. Thus, provision is made for the precursor layerto be uniformly and sufficiently subjected to a flow of reaction gasduring the sintering.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a cross sectional view of a furnace in accordancewith an embodiment of the invention.

FIG. 2 illustrates the fluid flow pattern within the furnace of FIG. 1,showing the substrate support oriented in a lowered position.

FIG. 3 illustrates the fluid flow pattern within the furnace of FIG. 1,showing the substrate support oriented in a mid-height position.

FIG. 4 illustrates the fluid flow pattern within the furnace of FIG. 1,showing the substrate support oriented in a raised position.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a cross-sectional view of a system in accordance with anembodiment of the invention. As illustrated, the system includes afurnace 1 with a furnace space defined by a furnace inner wall 1.1.Within the furnace space is a porous support 2 such as a porous plate.The support 2 is adapted to be raised and lowered within the furnacespace. Both of the side/outer edges of the support 2 are generally flushwith the furnace inner wall 1.1. A substrate or strip 3 having on itsupper side a precursor layer may be positioned onto the support 2. Forexample, the strip 3 may be drawn across the support 2 orthogonally tothe cross-section plane (e.g., it may be drawn from left to right acrossthe support from the perspective of FIG. 1). The furnace 1 furtherincludes at least one exhaust opening 4 formed in the furnace inner wall1.1. The exhaust opening may be centrally located above the strip 1. Theexhaust opening 4 is in fluid communication with the furnace space, and,as such, is configured to remove reaction gas from the furnace space.

Referring to FIGS. 2-4, in operation, reaction gas is fed into thefurnace 1 at a point below the support 2. The air travels toward thelower surface of the support 2, passing through its pores and around thestrip 3 with an HTSC precursor layer disposed on the upper surface ofthe support. This feeding creates a substantially laminar flow 6 towardsthe exhaust opening 4, above the support 2 and proximate the sides ofthe strip 3. A vortex zone 5 of an approximately onion-shapedcross-section is formed above the strip 3 within its flow shadow.

Thus, the continuous feeding of fresh reaction gas forms a laminar flow6 above the porous support and along the sides of the strip 3. Thevortex zone 5 forms above the strip 3 in the flow shadow of the strip.In the boundary region between the vortex zone 5 and the regions oflaminar flow 6 adjacent/lateral to the vortex zone, a continuousexchange of gas takes place between the vortex zone and the laminarflow. As a result, the vortex zone 5 is always sufficiently enrichedwith fresh reaction gas. In this manner, the vortices ensure good mixingof fresh and used reaction gas.

The support 2 may further be adapted to raise and lower to predeterminedpositions within the furnace space. As best seen in FIGS. 2-4, thesupport 2 may begin in a first position (FIG. 2) and be raised to asecond position (FIG. 3) and/or a third position (FIG. 4). Conversely,the support 2 may be lowered from the third position to either the firstor second positions. In this manner, the distance between the strip 3and the exhaust opening 4 can be varied by raising and lowering thesupport 2. The height at which the support may be positioned is notparticularly limited.

With a constant volume flow of the reaction gas, the size and shape ofthe vortex zone 5 (and thus the flow velocity in the vicinity of theprecursor layer and the degree of gas exchange between the vortex zoneand the region of laminar flow 6) can be adjusted.

Since part of the reaction gas fed into the porous support 2 does notpartake in an exchange with the vortex zone 5, it is preferred toconduct the reaction gas in a circuit, feeding it into the supportseveral times (e.g., the gas may be intermittently fed into the furnaceand through the support). Used reaction gas is removed from the circuitand replaced by fresh reaction gas.

Before being fed into the support 2, the reaction gas may be heated to apredetermined temperature, e.g., to at least to about the sinteringtemperature. By way example, when the gas has a temperature slightlyabove the sintering temperature, the gas will heat the strip 3 to thesintering temperature.

Similarly, at least a portion of the support 2 may be heated to apredetermined temperature. By way of example, the region of the support2 facing the entry side of the strip 3 into the furnace 1 may be heated.Heating the support 2 serves to heat the strip 3 rapidly to thesintering temperature.

A plurality of strips 3 may be drawn through the furnace in parallel andpreferably spaced from each other. The spacing between the strips 3preferably should be dimensioned so that a vortex zone 5 is formed aboveeach strip. In this way, a plurality of strips 3 may be sinteredsimultaneously, with each strip being sufficiently and uniformlysubjected to a flow of reaction gas.

Friction between the support 2 and the strip 3 may be reduced bydirecting gas of sufficient pressure between the support and the strip.In other words, the volume flow or the pressure of the gas fed into thesupport 2 can be adjusted so that reaction gas also emerges between thestrip 3 and the support 2, thereby reducing the friction occurringbetween the support 2 and the strip 3. The strip 3 can then be drawnacross the support 2 more easily, and less abraded matter is formed.This helps to inhibit blockage of the pores of the support, since fineabraded matter would be fed together with the circulating gas into thesupport 2 and block the pores thereof, at least after some time.

Preferably, the furnace 1 has at least one suction or vacuum meansdisposed above the support 2 for conducting-away reaction gas. Thesuction means, e.g., an exhaust mechanism, may extend parallel to thedirection of drawing-through the strip 3. It is particularly preferredto draw-off the reaction gas above the strip or strips 3. This causesthe cross-section of the vortex zone to become generally onion-shaped.The size of the vortex zone 5, the flow conditions within the vortexzone, and the gas exchange between the vortex zone and the laminar flowcan be adjusted by the position and the shape of the exhaust openings 4.

With exhaust openings 4 disposed to be parallel to the direction ofdrawing-through, an average concentration of fresh reaction gas that issubstantially constant along the direction of drawing-through isobtained in the vortex zone 5.

The flow of the reaction gas may be controlled particularly well whenthe exhaust openings 4 are slits that extend parallel to the directionof drawing-through, and/or when each strip drawn through the furnace isprovided with its own row of exhaust openings disposed in parallel withthe direction of drawing-through.

Thus, to perform the above-described method, a sintering furnace 1 issuitable that comprises a porous support 2 as a rest for a strip with anHTSC precursor layer, and at least one inlet and at least one outlet fora reaction gas. The support 2 communicates with the inlet for thereaction gas. Consequently, the reaction gas flows into the support 2and/or around the sides of the support, ultimately flowing around thestrip 3 as described above.

1. A sintering furnace comprising: a furnace having a furnace space; aporous support disposed within the furnace space, the porous supportconfigured to support a substrate having an HTSC precursor layer; atleast one inlet operable to direct reaction gas through the poroussupport; and at least one outlet operable to remove reaction gas fromthe furnace space.
 2. The sintering furnace of claim 1, wherein theinlet is disposed within the furnace at a point below the support. 3.The sintering furnace of claim 2, wherein: the outlet includes a vacuummechanism; and the reaction gas is directed from the inlet and throughthe porous support, and then is drawn from the furnace space by thevacuum mechanism.
 4. The sintering furnace of claim 1, wherein theoutlet comprises at least one suction mechanism disposed above theporous support, the suction mechanism extending generally parallel tothe direction in which the substrate is drawn through the furnace. 5.The sintering furnace of claim 1 further comprising a heating mechanismoperable to heat the gas to a predetermined temperature.
 6. Thesintering furnace of claim 1 further comprising a heating mechanismoperable to heat the porous support.
 7. The sintering furnace of claim1, wherein: the substrate comprises a first surface including theprecursor layer and a second surface facing the support; and frictionbetween the support and the second surface of the substrate is reducedby directing gas of sufficient pressure between the support and thesubstrate.